Reduced fracturing of intermetallic particles during crack propagation in age hardening Al-based alloys due to PFZs

Based on a shear lag model approach, a simple analytic model for the stress shielding of intermetallic particles due to the presence of a weakened precipitate free zone (PFZ) is derived. The PFZ desensitises the material to the breaking of particles. For the S and θ phase particles in the 2091 aluminium based alloy, particles with average sizes in the range 3-15 μm receive effective shielding from matrix stresses, which raise the matrix stress required to break the particle, and causes a propensity for larger particles to break at smaller applied macroscopic stress.